Ceramics and polymers are attractive candidate materials for MEMS applications because of the wide range of properties that can be obtained, and the promise of improved performance as compared to the existing materials set for MEMS. A challenge in the fabrication of ceramic MEMS is prohibiting cracking that can occur during processing. For example, this is significant in the development of a microcasting fabrication technique from a polymer precursor for silicon carbonitride (SiCN) MEMS. In this case, shrinkage mismatch between the SiCN structure and the microfabricated mold during thermal processes leads to significant stresses that can crack the ceramic structure. Here, we propose an approach to overcome this problem that relies on demolding prior to the large shrinkage mismatch thermal processes, which itself is a nontrivial challenge. To this end, we propose and describe a microforging process that facilitates demolding and show representative results for numerous SiCN ceramic microstructures.

Application of microforging to SiCN MEMS fabrication

Films of silicon carbonitride of variable composition are prepared by the method of plasmochemical decomposition of tetramethyldisilazane, hexamethyldisilazane, and hexamethylcyclotrisilazane in the mixture with helium in the temperature range of 373–973 K. The chemical composition of the low temperature films (373–673 K) is described by the formula SiCxNyOz:H, whereas that of high temperature films, by the formula SiCxNy. The films of silicon carbonitride are found to be a nanocomposite material containing an amorphous part and nanocrystals, whose structure is close to the phase α-Si3N4. Films of the composition SiCxNyOz:H are promising as low-k interlayer dielectrics in ultra-large scale integrated circuits of new generation, as well as protecting antireflective coatings and light-emitting diodes.

From organosilicon precursors to multifunctional silicon carbonitride

During the last years the interest in silicon and boron carbonitrides developed remarkably. This interest is mainly based on the extraordinary properties, expected from theoretical considerations. In this time significant improvements were made in the synthesis of silicon carbonitride SiCxNy and boron carbonitride BCxNy films by both physical and chemical methods. In the Si–C–N and B-C-N ternary systems a set of phases is situated, namely diamond, SiC, ┚-Si3N4, c-BN, B4C, and ┚-C3N4, which have important practical applications. SiCxNy has drawn considerable interest due to its excellent new properties in comparison with the Si3N4 and SiC binary phases. The silicon carbonitride coatings are of importance because they can potentially be used in wear and corrosion protection, high-temperature oxidation resistance, as a good moisture barrier for high-temperature industrial as well as strategic applications. Their properties are low electrical conductivity, high hardness, a low friction coefficient, high photosensitivity in the UV region, and good field emission characteristics. All these characteristics have led to a rapid increase in research activities on the synthesis of SiCxNy compounds. In addition to these properties, low density and good thermal shock resistance are very important requirements for future aerospace and automobile parts applications to enhance the performance of the components. SiCxNy is also an important material in microand nano-electronics and sensor technologies due to its excellent mechanical and electrical properties. The material possesses good optical transmittance properties. This is very useful for membrane applications, where the support of such films is required (Fainer et al., 2007, 2008; Mishra, 2009; Wrobel, et al., 2007, 2010; Kroke et al., 2000). The structural similarity between the allotropic forms of carbon and boron nitride (hexagonal BN and graphite, cubic BN and diamond), and the fact that B-N pairs are isoelectronic to C-C pairs, was the basis for predictions of the existence of ternary BCxNy compounds with notable properties (Samsonov et al., 1962; Liu et al., 1989; Lambrecht & Segall, 1993; Zhang et al., 2004). This prediction has stimulated intensive research in the last 40 years towards the synthesis of ternary boron carbonitride. BCxNy compounds are interesting in both the cubic (c-BCN) and hexagonal (h-BCN) structure. On the one hand, the

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Compilation on Synthesis, Characterization and Properties of Silicon and Boron Carbonitride Films

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane (Et 2N)3SiH (TDEAS) in the temperature region 373–1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300–1300 K and pressure interval P tot 0 from 1 × 10−2 to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-Si3N4 phase and of carbon inclusions has been found in the layers.

Tris(diethylamino)silane—A New Precursor Compound for Obtaining Layers of Silicon Carbonitride

Influence of carbon on stability, mechanical property, electronic structure, and lattice dynamics of silicon carbonitride

Silicon carbonitride monoliths derived from polymer powder compacts via polymer pyrolysis represent a new class of structural ceramic materials due to the complete coalescence of the powder particles during polymer decomposition and the formation of a uniform ceramic matrix free from any grain boundaries or secondary phases. The submicron pore channel system penetrating the material can be minimized in volume by infiltration of liquid polysilazane solution or by post-HIPing so that relative densities of 96% can be reached. The monoliths are oxidation resistant up to 1600°C in air due to the formation of a highly pure silica oxidation layer and they exhibit a creep rate of 1.10 -6 s -1 at 1650°C and 90 MPa load. Initially x-ray amorphous silicon carbonitride can be crystallized in nitrogen or in air to form Si 3 N 4 /SiC or Si 3 N 4 /SiC/C nanocomposites

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R. Riedel

Papers

Silicon carbonitrides - A novel class of materials